1. Technical Field
The present invention relates to a piezoelectric thin film elemental device using a piezoelectric thin film, and further specifically relates to the piezoelectric thin film elemental device having the piezoelectric thin film of an alkali niobate base perovskite structure on a silicon substrate, and to a sensor and an actuator using the piezoelectric thin film elemental device.
2. Description of Related Art
A piezoelectric substance is processed into various piezoelectric elemental devices according to various purposes, and is widely utilized as functional electronic components such as an actuator in particular for operating the piezoelectric elemental device by adding voltage thereto, thereby generating deformation, and reversely a sensor for detecting a physical amount from the voltage generated from the deformation of the piezoelectric elemental device. As the piezoelectric substance utilized for the purpose of use of the actuator and the sensor, a dielectric substance made of a lead-based material having excellent piezoelectric characteristics, and particularly a PZT-based perovskite ferroelectric expressed by a compositional formula: Pb(Zr1−xTix)O3 called PZT has been widely used heretofore, which is normally formed by sintering an oxide composed of individual elemental devices.
At present, as downsizing and higher performance of each kind of electronic component is progressed, the downsizing and higher performance is also required in the piezoelectric elemental device. However, in a piezoelectric material manufactured by a manufacturing method typified by a sintering method, being a method performed conventionally, as its thickness becomes thinner, particularly as the thickness becomes closer to the thickness of about 10 μm, this thickness becomes closer to the size of a crystal grain constituting the material, and its influence can not be ignored. This involves a problem that variation and deterioration of the characteristics is remarkable, and in order to avoid this problem, a forming method of the piezoelectric substance applying a thin film technique in place of the sintering method has been studied in recent years. In recent years, a PZT thin film formed on a silicon substrate by a sputtering method is put to practical use as a piezoelectric thin film for a supersensitive gyroscope (angular velocity sensor) (for example, see patent document 1).
Meanwhile, a piezoelectric sintering body and the piezoelectric thin film composed of PZT contains about 60 to 70 wt % of lead, and this is not preferable from an ecological viewpoint and from an aspect of pollution control. Therefore, development of the piezoelectric substance not containing lead is desired from the consideration of an environment.
Currently, various non-lead piezoelectric materials have been examined, and among them, sodium potassium niobate expressed by a compositional formula: (K1−xNax)NbO3 (0<x<1) (referred to as KNN hereafter in some cases) is given as an example. The KNN is a material having a perovskite structure, showing relatively excellent piezoelectric characteristics as a non-lead material, and therefore is expected as a dominant candidate of the non-lead piezoelectric material.
(Patent document 1)
    Japanese Patent Laid Open Publication No. 2005-203725
Deposition of the KNN thin film on the silicon substrate is tested, by a deposition method such as a sputtering method and a PLD, being a pulsed laser deposition method, or a laser ablation method, and in some cases, there is a report that piezoelectric constant d31=−100 pm/V, being the characteristic of a practicable level is realized. However, the piezoelectric constant is approximately d31=70 to −75 pm/V, if reproducibility and characteristic variation in a substrate surface is taken into consideration.
The piezoelectric constant d31 of the PZT thin film currently used in a product is about −90 to −100 pm/V, and if compared with this value, the piezoelectric constant d31 of the KNN thin film is still in a state of a small value. In order to widely apply the KNN thin film to an ink jet printer head, and so forth, the piezoelectric constant d31 must be improved up to −90 pm/V or more.